| 摘要 |
PURPOSE:To obtain a picture with a proper density by properly eliminating a background picture of an original. CONSTITUTION:An analog switch AS1 is turned off by an AND signal between an AEON signal representing automatic detection of background density (high level) or representing a fixed level as the detection value of background density (low level) and a PEAK signal representing the background density in terms of a detection width. A voltage of an original picture signal Vin is detected as a background peak voltage VPK by differential amplifiers A1, A2, A3 or the like and the result is outputted via an analog switch AS4 as a reference voltage for an A/D converter. The AEON signal and the PEAK signal are set when the original is carried forward and the background level VPK is detected and then they are cleared. After the original is carried reverse, the original is carried forward and read from its head and the background is eliminated by using the background level VPK. |
